Wide band antenna for satellite navigation and related problems



OCII. 13, 1970 v, c, s rr JR 3,534,378

WIDE BAND ANTENNA FOR SATELLITE NAVIGATION AND RELATED PROBLEMS FiledDoc. 13, 1967 INVENTOR. VALOR C. SMITH JR.

ATTORNEYS United States Patent C) I 3,534,378 WIDE BAND ANTENNA FORSATELLITE NAVI- GATION AND RELATED PROBLEMS Valor C. Smith, Jr., LaMesa, Calif., assignor to Chu Associates, Inc., Littleton, Mass., acorporation of Massachusetts Filed Dec. 13, 1967, Ser. No. 690,257 Int.Cl. H01q 9/30 US. Cl. 343-828 4 Claims ABSTRACT OF THE DISCLOSURE Thisdisclosure deals with a novel wide band antenna that is particularlyadapted for receiving satellite transmissions as for navigationpurposes, the antenna being adapted through novel conductive-elementconfigurations, to produce substantially omni-directional horizontalcoverage and upwardly tilted toroidal vertical coverage substantiallyuniformly over the wide band.

The present invention relates to wide band antennas and is moreparticularly concerned with relatively lightweight antenna structuresadapted simultaneously to receive frequencies over a wide frequencyrange substantially omni-directionally in the horizontal plane, but withan upwardly tilted toroidal vertical pattern.

In such applications as the reception of multiplefrequency satellitenavigational signals, including signals in the lower frequency VHF band(such as of the order of 150 mHz.) and relatively high frequencies inthe UHF region (such as 400 mHz.), it is desirable to avoid thereception of spurious reflections that are returned to the antenna asearth-reflected satellite transmissions. For this purpose, the verticalradiation pattern or coverage should be directed upward, as in the formof an upwardly tilted toroidal pattern, while the horizontal coverageshould enable reception from any direction. While it is difficult toprovide substantially the same pattern or coverage with a singlestructure over such widely different frequencies, yet, for such criticalpurposes as navigation and the like, it is vitally important that theradiation patterns be very closely the same irrespective of thefrequencies being received.

It is to the solution of this problem that the present invention isprimarily directed; it being a primary object of the invention toprovide a new and improved wide band antenna of the character abovedescribed that shall discriminate against spurious ground-reflectedtransmissions and shall provide substantially the same radiationpatterns irrespective of the frequency being received, over wide limits.

A further object is to provide a novel antenna of the characterdescribed that while particularly suited for reception purposes is alsouseful for transmission and is of more general applicability as well.

Other and further objectives will be explained hereinafter and areparticularly pointed out in the appended claims.

In summary, however, the invention preferably embodies a cylindricalconductive structure cooperating with a ground plane member and providedwith current-suppressing means of appropriate dimensions and geometricarrangement to enable the simultaneous application to the antenna ofcurrents of widely different frequencies with substantially the sameomnidirectional horizontal coverage and upwardly tilted toroidalvertical coverage. Though the words horizontal and upwar are usedherein, these are, of course, to be understood to be relative andillustrative only. Preferred constructional details are later set forth.

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The invention will now be described with reference to the accompanyingdrawing, the single figure of which is a schematic isometric view of apreferred embodiment.

Referring to the drawing, the antenna of the invention is showncomprising a cylindrical conductive member having a first relativelylarge diameter section 1 that terminates in a shorter smaller-diametersection 1'. The bottom end of the member 1-1' is shown insulatinglyspaced at 3 from a conductive ring-like lower extension 5 from whichdifferent-length conductors 7 and 7' radially extend in spoke-likefashion to define a common ground plane.

In accordance with the preferred embodiment of the invention, the lengthof the cylindrical member 1-1' corresponds substantially to thehalf-wavelength of one of the frequencies near the low end of the wideband of frequencies with which the antenna is simultaneously to operate.The diametric paths provided by the substantially co-planar groundconductors 77 correspond substantially to a similar half-wavelength,while the paths defined by the shorter conductors 7 correspondsubstantially to the half-wavelength of one of the high frequencies nearthe upper end of the Wide band of frequencies. It has been found thatthe alternate substantially equi-angular spacing of the long and shortradial conductors 7, 7' provides a ground plane that acts in asubstantially uniform manner for all frequencies within the band.

The cylindrical conductive member 1-1' may receive the lower frequenciesof the band, being connected by the coaxial line 22 to act as atravelling-wave monopole with currents fed across the slot 3 between theground plane 7-7' and the member 1-1'. In accordance with the invention,however, only the lower portion of the section 1 of the cylindricalconductor 1-1 is similarly employable for frequencies near the high endof the wide band. This result is attained by high-frequencycurrentsuppressing and phasing conductive stubs 4, shown conicallysurrounding the upper portion of the section 1 at a distance from thelower end thereof corresponding substantially to a half-wavelength of afrequency near the upper end of the said wide band. The angle of thecone may be of the order of forty-five degrees, more or less. It hasbeen found that the use of such conductors 4, in the geometryillustrated and described, will effectively render the upper portion ofthe cylindrical section 1 and its extension 1' ineffective insofar asthe propagation of high-frequency currents is concerned, while producingno substantial impeding effect to the propagation of the low-frequencycurrents-and this, while generating substantially the same upwardlytilted toroidal vertical coverage or pattern at both the low and highends of the band, and consistent with similar omni-directionalhorizontal coverage.

As an example, an antenna of the type described has been successfullyoperated for transit satellite transmissions in the frequency band from-400 mHz. with a cylindrical section 1 about 5% inches in diameter andabout 29 inches in length and an extension section 1 about 11 inches inlength and inch in diameter; these relative dimensions and lengthsproducing an excellent impedance match to a 50 ohm-coaxial line 2-2. Thecurrent-suppressing and phasing elements 4 were disposed about 16 inchesfrom the lower end of the member 1. The upwardly directed verticaltoroidal pattern at 30 of elevation varied only about /2 decibel fromthe low frequency limit of 150 mHz. to the high frequency limit of 400mHz.

In order to insure the desired travelling-wave propagation and impedancematching, appropriate choke sections or transformers, as schematicallyillustrated at 6,

have been employed. These chokes may be coaxial or lumped-circuitdevices.

Further modifications will also occur to those skilled in this art andall such are considered to fall within the spirit and scope of theinvention as defined in the following claims.

What is claimed is:

1. A wide band antenna for producing substantially omni-directionalhorizontal coverage and an upwardly tilted toroidal vertical coveragehaving, in combination, a cylindrical conductive means of lengthcorresponding substantially to the half-wavelength of a frequency at thelow end of the said wide band, ground plane means comprising a pluralityof substantially co-planar conductors of diflerent lengths providingpaths of substantially the half-wavelengths of frequencies at both thelow and high ends of the said wide band and slightly spaced from one endof the cylindrical conductive means to define a slot there-between,current-suppressing means disposed along said cylindrical conductivemeans a distance from said one end corresponding substantially to ahalf-wavelength of a frequency at said high end of the band in order tosuppress the propagation of such high-frequency currents beyond saiddistance, and means for simultaneously feeding currents of differentfrequencies lying within said hand between said ground plane and saidone end of the cylindrical conductive means across said slot.

2. A wide band antenna as claimed in claim 1 and in which said groundplane conductors comprise spaced radially conductors.

3. A wide band antenna as claimed in claim 1 and in which saidcurrent-suppressing means comprises a plurality of spaced conductorsdefining an upwardly directed conical surface about said cylindricalconductive means.

a 4. A Wide band antenna as claimed in claim 1 and in which saidcylindrical conductive means comprises two sections of widelydifierent-diameter cylinders, the first section being longer and ofgreater diameter than the second section.

References Cited UNITED STATES PATENTS 2,267,889 12/1941 Aubert 3438.262,724,052 11/1955 Boyer 343-830 X HERMAN K. SAALBACH, Primary ExaminerM. NUSSBAUM, Assistant Examiner U.S. Cl. X.R.

